Prior art force attenuation apparatus for aircraft seats have generally included a compressible corrugated aluminum cylinder in the seat height adjustment mechanism to serve as an energy absorber. Accordingly, under high impact landing conditions, energy is dissipated through the permanent deformation, or crushing, of the energy absorber.
Representative of prior art force attenuating apparatus for a landing gear assembly is the two-stage system of energy absorbers disclosed in U.S. Pat. No. 3,716,208. In that apparatus, the first stage of energy absorption involves driving a piston in an oil filled cylinder to move oil through control orifices and thereby reduce the forces applied to the airframe through the landing gear. The second stage of energy absorption involves actual deformation of the struts which connect the landing gear to the airframe.
Other means for attenuating forces generated upon landing of an aircraft with high vertical velocity is the crash attenuation landing gear disclosed in U.S. Pat. No. 3,997,133. In that patent, there is disclosed, in combination with a cushioned strut, an energy dissipation structure in the form of a relatively thin walled aluminum cylinder. The apparatus further includes a ring having a plurality of radial, upwardly facing cutter blades for engaging the inner wall of the cylinder to do mechanical work upon movement of the cylinder relative to the ring. More specifically, the mechanical work done by the ring is that of slicing the cylinder into longitudinal strips as relative movement takes place.
A modification of the cylinder-cutter structure is disclosed in the patent and involves the utilization of a flaring structure in place of the cutter ring. In the modified apparatus, as the cylinder is forced downward over the working surface of the flaring structure, the edges of the cylinder are flared and the cylinder is torn. The flaring operation absorbs energy, and thus attenuates forces.
Examples of energy absorbing systems as a vehicle bumper are those presently installed on passenger vehicles. Basically, such systems are hydraulic filled energy absorbing cylinders.
The application of reinforced plastics to automotive structures, where such structures provide crashworthiness, is the subject matter of a study sponsored by the U.S. Department of Transportation as reported in Report No. DOT HS-801 771, entitled "Feasibility Study of Plastic Automotive Structures". This report presents an in depth study of the use of plastic automotive structure to protect the passenger compartment during a frontal impact.
In accordance with the present invention, force attenuation apparatus is provided that may be readily adapted for use in various portions of an aircraft or other vehicle to attenuate forces developed during high velocity impact landing or stopping, by absorbing energy.
Force attenuating apparatus in accordance with the present invention utilizes an elongate member of composite, fibrous material disposed between an anvil at one end of the elongate member and means for applying a force to the opposite end of the composite elongate member. The force attenuation apparatus of the present invention dissipates energy as the means for applying force to the elongate member progressively crushes the member onto the anvil.
In accordance with the present invention, the elongate composite member is a closed or open section column whose wall comprises a fiber reinforced plastic whose fibers are at various angles with respect to a plane extending transverse to an axis of the elongate member. The anvil onto which the elongate member is crushed may have a flat surface or may be a conic with a positive or negative coning angle.
Suitable composite material for the elongate member of the force attenuation apparatus has been found to include graphite, fiberglass, boron and aramid type fibers in a plastic resin.
The present invention is envisioned as being utilized in various applications involving the attenuation of forces and dissipation of energy. Among such applications are energy absorbing landing gear assemblies for aircraft, energy absorbing seats for aircraft and other vehicles, energy absorbing vehicle bumpers and various other like applications.